Rat pituitary levels of oxytocin were elevated by a single injection of estrogen. This treatment did not affect pituitary levels of vasopressin. However, a second injection of estrogen or an injection of progesterone to estrogen-pretreated rats raised vasopressin levels. Norepinephrine levels and turnover in the paraventricular nucleus were reduced by hormone treatments that elevated pituitary vasopressin, while norepinephrine in the supraoptic nucleus did not change. Transection of the ascending ventral noradrenergic bundle reduced norepinephrine levels in the hypothalamic nuclei and also reduced pituitary vasopressin, but markedly elevated pituitary oxytocin.